MANILA (UPDATED) - Embattled Chief Justice Maria Lourdes Sereno has sought the compulsory disqualification of Associate Justice Teresita Leonardo-De Castro from proceedings on a petition seeking to nullify her appointment.

The Sereno camp in a statement said De Castro should inhibit from proceedings on the "quo warranto" petition filed by Solicitor General Jose Calida against the chief magistrate, saying she has “repeatedly manifested actual bias, if not personal animosity” towards her.

The Chief Justice filed a 30-page motion before the High Court arguing that De Castro had "already prejudged" the issue regarding the validity of her appointment as head of the judiciary in 2012.

“With due respect, the Chief Justice has reasonable grounds to believe that Justice Leonardo-De Castro had already prejudged the issue regarding the validity of the Chief Justice’s nomination and subsequent appointment in 2012,” Sereno said.

“It does not appear that Justice Leonardo-De Castro can decide this case with the cold neutrality required of an impartial judge. Independent of such presumption, it is respectfully submitted that there is clear and convincing evidence to show that she has prejudged the very issue in this case to the respondent’s prejudice,” she added.

De Castro is the fifth magistrate that Sereno wants out of deliberations on the quo warranto case.

The chief magistrate's camp earlier filed separate recusal pleas against her colleagues Associate Justices Diosdado Peralta, Lucas Bersamin, Francis Jardeleza and Noel Tijam, saying they had shown “actual bias” against her.

• Sereno accuses 4 SC colleagues of bias

The top magistrate's camp noted that De Castro must inhibit herself pursuant to the New Code of Judicial Conduct, which “mandates the inhibition of a judge who is unable to decide the matter impartially or who may appear to a reasonable observer to be unable to decide a matter impartially.”

“Her (De Castro) disqualification is thus mandatory under the pertinent provisions of the Canons of Judicial Ethics, the New Code of Judicial Conduct, the 1989 Code of Judicial Conduct, and the Internal Rules of the Supreme Court,” Sereno said.

Sereno also warned that De Castro’s refusal to inhibit would violate her right to due process.

The High Court is set to hold oral arguments on Calida's petition on April 10 in Baguio City.

• Sereno to attend oral arguments on quo warranto plea

Sereno was ordered to attend the proceedings, a request the chief magistrate would heed, according to her spokesperson.

• Sereno to attend oral arguments on quo warranto plea

All 5 associate justices Sereno sought to bar from the proceedings had testified against her during hearings of the House of Representatives justice committee on the impeachment complaint filed by lawyer Lorenzo Gadon.

In testifying against Sereno, De Castro had questioned the chief magistrate's order to create a Judiciary Decentralized Office for Central Visayas in 2012, saying this was not compliant with an en banc decision.

• De Castro questions Sereno order creating JDO

Tension between Sereno and De Castro was also apparent at a public event last month, when the latter reprimanded the Chief Justice for talking about her impeachment woes at a gathering of judges.

• De Castro censures Sereno speech, cites pending court case

Following the incident, Sereno downplayed reported infighting between her and magistrates of the high court.

"In any organization, there will be occasions when these kinds of problems will arise, but I'm sure that in time, when the dust settles, we will all come around again and move forward to be the bringer of justice to the people," she said.

• Sereno downplays SC 'infighting'

The top magistrate has been on leave from her duties at the Supreme Court since last month in preparation for a possible impeachment trial. The High Court en banc had reached such consensus for "several reasons" no longer bared.

• SC justices reached consensus Sereno should take indefinite leave